The production of hydrocarbon gas products via anaerobic fermentation often results in a fermenter off-gas containing various amounts of impurities as part of the fermentation process (e.g. water vapor from the fermentation media, carbon dioxide as a respiration product, as well as other organic bio-byproducts). In aerobic fermentation the fermenter off-gas also contains nitrogen and oxygen impurities from aeration.
While a wide variety of commercial products can be manufactured by fermentation processes, some efforts have been made on development of purification of fermentation hydrocarbon products from fermenter off-gas streams.
U.S. Pat. No. 8,324,442 discloses purification methods for fermentation derived gaseous isoprene compositions using chillers and flash drums in order to obtain a liquid isoprene enriched composition at temperatures below −35° C. In some embodiments, the method further comprises extracting hydrocarbon impurities at some point of the purification process using a modified zeolite membrane and/or molecular sieve wherein the modified zeolite and/or molecular sieves selectively adsorb isoprene and not the other hydrocarbons in the composition or vice versa (adsorb other hydrocarbons in the composition and not isoprene).
U.S. Pat. No. 8,569,562 discloses methods and apparatus for the purification of a bioisoprene composition from fermenter off-gas based on solvent extraction comprising one or more columns to remove volatile and/or bio-byproduct impurities resulting from fermentation.
The present invention provides a new fermentation hydrocarbon gas product separation and purification process based on a membrane system. In one aspect, the present invention provides a fermenter off-gas separation and purification process in order to obtain a fermentation product rich gaseous stream with at least 70% wt of the fermentation hydrocarbon product without working under low temperatures or using solvent.